Method of making silicon articles.



" anion,

THOMAS IB. ALLEN, OF NIAGARA FALLS, NEW YORK, ASSIGNOR TO THECARIBORU'NDUM COMPANY, OF NIAGARA FALLS, NEW YORK, A CORPORATION OFPENNSYLVANIA.

METHOD OF MAKING- SILICON ARTICLES.

No Drawing.

T all whom it may concern:

Be it known that I, THOMAS B. ALLEN, a resident of Niagara Falls,Niagara county, State of New York, have invented a new and usefulImprovement in Methods of Making Silicon Articles, of whichthe'following is a full, clear, and exact description.

This invention has relation to a new and useful improvement in themethod of making silicon articles.

Heretofore, the production of silicon articles by casting molten metalinto the desired shape has been attended with very great difficulties,which have been so great as to practically prevent the format-ion ofsuitable articles. The main difliculties in casting the ordinary moltenmetal have been, first, that the cast metal is very spongy and porous,being filled with blow holes and pin holes; second, that the castarticle is mechanically unsound, this being largely occasioned by thepresence of How marks due to the lapping of the metal which causes foldsin the surfaces of the cast silicon; and third, that the cast metal israther coarsely crystalline which tends to make the article mechanicallyweak. 7 I

I have discovered that electric furnace silicon and silicon alloys andcompounds contain dissolved silicon dioxid and dissolved nitrogen andoxygen, and that by removing these substances, I am able to obtaincastings which are stronger, denser and more perfect than any castingsso far obtained. I have further discovered that I can obtain theimprovements and remove the-impurities by means of a large number ofsubstances, such as the alkali metals, the alkaline earth metals,magnesium, vanadium, titanium,

aluminum, boron, etc., and in general, any

element which has a combining heat with the impurities, which is greaterthan that of silicon. To obtain especially advanta geous results, Ipreferably use a material, :uch as calcium, magnesium, vanadium, etc.,vvhich, besides acting as a deoxidizing agent, :an act as adenitrogenizing agent. I may, iowever, also add an element, such assolium, to remove the oxygen or oxids, and a. mbstance, such asvanadlum, to remove the iitrogen or nitrids.

I will now describe a preferred method of arrying out my invent-ion withreference to Specification of Letters Patent.

Application filed June 26, 1911.

Patented Sept. 3, 1912. Serial No. 635,500.

for about one to two hours, having preferably placed a layer of coke onthe surface of the silicon to prevent loss by oxidation andvolatilization. When the silicon is in a very fluid condition, I removethe crucible from the furnace, skim off the coke and add the magnesiumto the molten silicon in the form of a fine powder or in small lumps bymeans of an implement commonly called a phosphorizer. I have found thatI can obtain the desired results by adding from one-half per cent. tothree per cent. magnesium and I contemplate adding only such a quantityof this substance which will combine with the impurities and pass off tothe surface of the silicon as a slag. The magnesium silicate formed whenmagnesium is used is readily fusible and comes to the surface of thefused silicon. When the silicon shows no further reaction due tomagnesium and is in a quiescent condition, I preferably pour it from-thebottom of the crucible in order to prevent any of the slag from thesurface getting into the molten silicon.

In making the mold of the desired shape for the silicon article, Iprefer to use what is commonly known as a dry sand mold and to coat thesurfaces of this mold with which the molten silicon comes in contactwith talc. I have further found it desirable to pour the metal into themold through a gate entering at the bottom of the mold and to use acomparatively large riser, so that the casting cools under considerablefluid pressure. By this means I aid the production of dense soundcastings. The articles produced in this manner are mechanically soundand show a marked absence of blow holes and flow marks. The metalcrystallizes in very fine crystals and shows a marked interpenetrationof the same which causes the articles produced to have considerablemechanical strength.

It will be evident to others skilled in the art of making castings thatI may make many changes in the described method with out departing fromthe spirit of the invention. Further, by the term silicon used siredform, substantially as described.

2. The method of removing impurities from silicon, which consists inadding thereto an element having a combining heat with said impuritieshigher than the combining heat of silicon, substantially as described.

3. The method of making silicon tastings, which consists in adding anelement whose oxids has a higher heat of formation than the oxids ofsilicon and whose nitrid has a higher heat of formation than the nitridof silicon, removing the reaction products, and pouring the moltensilicon into the desired form, substantially as described.

4. The method of making silicon articles, which consists in adding tomolten silicon an element whose afiinity for oxygen and nitro gen isgreater that that of silicon, removing the reaction products, andpouring the molten silicon into the desired form, subsantially asdescribed. 5

5. The method of making silicon articles, which consists in adding tosilicon an element whose oxid has a higher formation heat than oxid ofsilicon, and an elementwhose nit-rid has a higher formation heat thannitrid of silicon, removing the reaction products, and casting themolten silicon into the desired form, substantially as described.

6. The method of making silicon articles, which consists in adding tosilicon an element whose formation heat with the impurities in themolten silicon is greater thanthat of silicon, removing the reactionproducts, and casting the molten silicon into the desired form underpressure, substantially as described.

7. The herein described method of treating molten silicon to removetherefrom silicon dioxid and nitrogen and oxygen, which consists inadding thereto a metal which will combine with said impurities to form aslag, substantially as described.

8. The herein described method of treating molten silicon to removetherefrom silicon dioxid, andnitrogen and oxygen, which consists inadding thereto an alkaline metal, which willcombine with said impuritiesto form a slag, substantially as described.

9. The herein described method of treating molten silicon to removetherefrom silicon dioxid and nitrogen and oxygen, which consists inadding thereto magnesium, which will combine with said impurities toform a slag; substantially as described.

10. The herein described method of treating molten silicon to removeimpurities therefrom, which consists in tapping the metal from thefurnace with a crucible, and

heating it to bring it to a highly fluid condition, protecting the metalWhile being so heated to prevent oxidation and volatilization losses,and then adding thereto a metal which has a combination heat with theimpurities in the silicon higher than the combining heat of silicon, andseparating the silicon from the resulting slag, substantially asdescribed.

11. The herein described method of making articles in which silicon isthe principal constituent part, which consists 111 tapping moltensilicon into a vessel and heating the same until the silicon is in avery fluid condition, then adding thereto an element which has a. higherformation heat with the 1mpurities existing in the silicon than ofsilicon, and which will unite with said 1 m purities to form a slag, andthen separating the purified silicon and slag and casting the silicon,substantially as described.

In testimony whereof, I have hereunto set my hand.

THOS. B. ALLEN. Witnesses:

L. B. COULTER, F. T. PIERCE.

